Oil recovery by steam injection and pressure reduction



1968 J. VAN LOOKEREN 3,367,419

OIL RECOVERY BY STEAM INJECTION AND PRESSURE REDUCTION Filed Sept. 20, 1965 FIG.

FIG.

FIG. 3

FIG; 4

I NVENTOR JOHANNES VAN LOOKEREN BY: gourd "='r-". a IS ATTORNEY United States Patent 3,367,419 OIL RECOVERY BY STEAM INJECTIQN AND PRESSURE REDUCTION Johannes van Lookeren, Rijswijk, Netherlands, assignor to She'd Oil Company, New York, N.Y., a corporation of Delaware Filed Sept. 20, 1965, Ser. No. 488,578 Claims priority, application Great Britain, Sept. 28, 1964, 39,511/64 9 Claims. (Cl. 16611) ABSTRACT OF THE DISELOSURE A method of producing hydrocarbons from a permeable, hydrocarbon-bearing formation penetrated by at least one injection well and at least one production well, into which formation hot fluid is injected through the injection well, and hydrocarbons are produced through the production well. The pressure within the pores of the part of the formation contacted by the hot fluid is reduced to a value lower than the pressure within the pores of the rest of the formation subsequent to the breakthrough of the hot fluid into the production well by decreasing the resistance to flow in the part of the formation surrounding the production well.

The present invention relates to a method of producing hydrocarbons from a permeable, hydrocarbon-bearing formation, into which at least one injection well and at least one production well penetrate.

In particular the present invention relates to a method of producing hydrocarbons from a permeable, hydrocarhon-bearing formation, in which hot fluid is injected into the said formation through an injection well penetrating the formation and hydrocarbons are produced from said formation through a spaced production well penetrating the same formation. Part of the heat of the hot fluid is transferred to the formation and the hydrocarbons therein, thereby decreasing the viscosity of the hydrocarbons which aids oil production and this method is an improved method of increasing the efficiency of such hot-fluid drives.

According to the invention, a method for producing hydrocarbons from a permeable, hydrocarbon-bearing formation, which is penetrated by at least one injection well and at least one production well, a hot fluid is injected through the injection Well into the formation and hydrocarbons are produced from the formation through the production well and after the hot fluid has broken through in the production well the pressure is reduced within the pores of the part of the formation contacted by the hot fluid to a value lower than the value of the pressure within the pores of the rest of the formation.

The term hot fluid is to be understood to mean a fluid having a temperature which is higher than the temperature of the formation into which it has to be injected. It could be a heated gas or liquid such as steam or hot water and could contain surfactants.

In the known processes, the pressure of the injection fluid is higher than the original formation pressure and the hydrocarbons from the heated Zone of the formation are often driven past the production well(-s) during the drive and are not recovered. However, in the present process, the pressure within the part of the formation which is heated is reduced, subsequent to breakthrough of the hot fluid, to a pressure lower than the pressure prevailing within the rest of the formation. By this technique, the hydrocarbons are recovered in the zone bounded by the injection and production wells and also, hydrocarbons originating from other parts of the formation outside the actual flow zone of the hot fluid are subsequently recovered via the production Well(s). Thus, by this new method, a greater amount of hydrocarbons can thus be obtained per production well.

Preferably, the hot fluid used in the present process is in the form of steam, either wet, dry or superheated. If desired, the steam may be mixed with gases or liquids, such as water, to increase its recovery efliciency.

In the practice of this invention, the pressure within the pores of the part of the formation contacted by the hot fluid may be reduced after the breakthrough of the hot fluid into the production well, by decreasing the resistance to flow in the part of the formation surrounding the production well, and/ or by decreasing the resistance to flow at the outlet of the production well, and/or by increasing the pumping rate of a pump provided in the production Well. The pressure within the pores of the part of the formation contacted by the hot fluid may also be reduced by decreasing the rate of injection into the injection well while maintaining a constant output at the production well. If desired, any of these measures may be carried out simultaneously.

The invention may be carried into practice in various ways but certain aspects will now be further described by way of example with reference to the accompanying drawings, in which:

FIGURE 1 shows schematically a section of a permeable, hydrocarbon-bearing formation penetrated by an injection Well and a production well;

FIGURE 2 shows schematically a pattern of injection and production wells suitable for practicing the present invention;

FIGURE 3 shows schematically another pattern of wells which may be used in a formation for carrying out the present process; and

FIGURE 4 shows a section of a permeable, hydrocarbon-bearing formation containing an impermeable layer or 11streak and pener-tated by injection and production we s.

In FIGURE 1, the hydrocarbon-bearing formation 1 is bounded at the top by a substantially impermeable strata 2, and at the bottom by a substantially impermeable strata 3. An injection well 4 penetrates through the strata 2 and into the formation 1. At a spaced distance from this injection well 4, there is a second well which is designed to be used as a production well 5. Both wells 4 and 5 are provided with casing, tubing, liners and other equipment suitable for hot fluid drives between spaced wells. The usual techniques (such as heat treatments or fracturing methods) may be carried out in the surrounding formation to increase the productivity of the formation. All equipment, as well as the cementing layers, securing the casing strings in the formation, have been omitted from the drawings for the sake of simplicity. If desired, the production Well 5 may extend through the formation 2 and into strata 3 and have the production tubing located in the well in such a way that its suction openings are located below the bottom of the formation 1. This allows a liquid seal to be formed between the formation pore space and the interior of the production tubing, which limits the escape of hot fluids to the surface.

The well head of the injection well 4 communicates with a conduit 6 provided with a valve 7. Conduit 6 communicates with a source of hot fluid (not shown), such as a boiler or furnace for generating steam and/ or hot water. The hot fluids controlled by valve 7 can be fed from the source through conduit 6 and into formation 1 via injection well 4.

The wellhead of the production well 5 communicates via a conduit 8 with a tank (not shown) for the storage of the produced hydrocarbons. Conduit 8' has a shut-off valve 9 and pumping equipment (not shown) between 3 the valve 9 and the tank. Well 5 may also have downhole pumps.

If the steam is applied as a hot fluid in carrying out the method according to the invention, it may be superheated, dry or wet. Since the devices for generating such steam are well known, they are not described herein. The steam may be mixed with other fluids either gaseous such as air, or liquid such as water, or both.

The method according to the invention is, in the arrangement of wells as shown in FIGURE 1, carried out as follows:

Steam is applied as the hot fluid and injected into the formation 1 via the conduit 6, the valve 7 and the injection well 4. The pressure of the steam on entry into the formation 1 is higher than the pressure prevailing in the pores of the formation 1. The steam drives part of the hydrocarbons in the direction of the production well 5, and out of the formation 1 via the well 5, the conduit 8 and the valve 9. During this operation, the steam which is injected into the formation for the greater part thereof condenses thereby forming a condensation front. The position of this front is schematically shown in FIGURE 1 in position 10, indicated by a broken line, shortly after the start of the process, and in position 11, at some later stage.

To obtain a high production rate, the valve 9 is fully opened so as to reduce the resistance to flow as much as possible out of production well 5. The production rate may be further increased by pumping the hydrocarbons out of the well 5 by any one of the known methods. Of course, the rate at which the hydrocarbons are displaced out of the formation by the action of a pump arranged in the production well 5 influences the pressure within the formation 1.

After a certain time, steam starts breaking through into the production well 5. The boundary which then exists between the steam zone and the zone in the formation pore space which is for the greater part filled with hydrocarbons, is schematically indicated by the line 12. Excessive steam production after this breakthrough is prevented by decreasing the off-take rate by limiting the pump rate in the well 5 or by throttling the valve 9.

Subsequent to the time steam passes between the two wells 4 and 5 over the condensation front 12, the pressure within the part of the formation which is in contact with the steam is gradually reduced to a value which is lower than the value of the pressure in the rest of the formation, preferably in the area of the production well 5. In practice, this will result in an injection pressure of the steam (measured after the steam has left the well 4 and entered the formation 1) which is less than the original formation pressure provided that the pressure outside the steam zone is not increased during the period before the breakthrough has occurred. Original formation pressure is to be understood as the pressure prevailing in the formation pore space prior to the injection of steam for carrying out the present process.

The same technique described above relative to the various pressures also applies when other hot fluids, e.g., hot water, are used for carrying out the process of this invention.

The desired decrease of pressure within the formation pore space that has been contacted by the hot fluid can be accomplished by a decrease in the injection rate of the hot fluid (e.g., by throttling valve 7), and/or from a decrease in the resistance to flow in the formation surrounding the production well 5 by fracturing the formation part around well 5 wherein a horizontal fracture is arranged at a low level in the formation, and/ or through the well 5 by further opening the valve 9 or increasing the pumping rate in the production well 5. Preferably, the valve 7 is gradually throttled and the valve 9 is gradually opened while the pumping rate is increased until the pressure reduction within the hot zone of the formation has been attained.

In another way, the injection of steam into the formation 1 may be stopped after steam breakthrough occurs, allowing the pore pressure in the hot zone of the formation to decrease by keeping the valve 9 open, or even further opening this valve or increasing the pumping rate. After the desired reduction of the pore pressure has been reached, steam injection is restarted via the injection well 4 at a restricted rate so that the pressure within the hot formation zone remains lower than the pore pressure in the rest of the formation.

The boundary between the steam zone and the zone in the formation pore space which is for the greater part filled with hydrocarbon, moves between the wells 4 and 5, from the position 12 occurring just after the breakthrough of the steam has taken place, to position 13. Subsequently, when the injection of hot fluid is resumed via well 4 and hydrocarbons are being recovered via well 5, the boundary progressively moves to the positions 14, 15 and 16. Further, in the part of the formation which is located on the remote side of the well 5 from the well 4, the boundary can possibly progress as indicated schematically by the lines 13', 14', 15' and 16 as the later stages of the process are carried out.

As a result of the reduction of the pressure within the warmed pore space of the steam swept zone of the formation 1, oil will flow from the cooler parts of the formation towards the hot zone thereof and into the area of production well 5.

The rate of flow depends on the amount of heat which is transferred from the hotter zone to the cooler zone and the boundary between the steam zone and the zone in the formation pore space which is for the greater part filled with hydrocarbon will find an equilibrium position, say at line 16'.

As a result of the pressure drop existing in the direction of the production well 5, hydrocarbons will be produced from a larger area around the production well 5 than with prior art processes.

The removal of hydrocarbons from the formation 1 via the production well 5 may be accomplished by any one of the known methods. Communication between the Well 5 and the pore space of the formation 1 may take place, e.g., via a liner arranged at the lower end of a casing provided in the well, or via perforations shot in the casing. The lifting of the hydrocarbons to the surface may be effected by pumping or gas lifting if natural forces and/or the forces generated by the hot fluid are insu cient for that purpose. These arrangements are not described in detail as they are well known and can be applied by the one skilled in the art as the circumstances dictate.

If impermeable or substantially impermeable streaks occur within the permeable formation 1, such as indicated by 20 in FIGURE 4, the production well 5 is preferably drilled through the said streak and is open at a level below the said streak, and if desired, above it also.

Although the present invention has been described with reference to FIGURE 1, being the application thereof in a formation into which a single injection well and a single production well penetrate, the invention is not limited thereto and would normally be practiced with multiple well patterns.

The present method may be applied with the same effect for recovering hydrocarbons from an underground formation in which more than one injection well and/or more than one production well penetrate. As shown in FIGURE 2, a complex row well pattern may be used in which the injection wells 4 arranged in a row 17, and the production Wells 5 are aligned in one or two rows (row 18 and/ or row 19) which run substantially parallel to the row 17 of the injection wells 4 but spaced therefrom.

Alternatively, the production wells 5, as shown in FIG- URE 3, can be located around a central injection Well 4. The extent to which the hydrocarbons have been removed from the formation in a lateral direction after the process has been applied, is schematically indicated by way of example in FIGURE 3 as well as in FIGURE 2 by the line 16. It will be clear that instead of six production wells arranged around a single injection well, one may use any other pattern or number of production wells 5. Further, it will be obvious that the patterns which have been shown by way of example may be duplicated or even multiplied in the same field for the production of hydrocarbons from a single hydrocarbon-containing formation. If desired, these patterns are arranged in such a way that the ultimate boundaries 16 to be reached by the processes carried out in the various patterns, do not intersect.

The flow of oil from the zone outside the boundary 16 to the production well(s) may, if desired, be supported by injecting drive fluids into injection wells which are located in the zone outside the boundary 16'. These fluids, such as hot or cold water, air, or steam increase the pressure in the said zone which promotes the flow of oil to the production well(s).

The advantage of the method according to the present invention resides in the fact that hydrocarbons are induced to flow to the production wells out of the formation as a result of the low pressure prevailing Within the hot fluid zone. This is just the reverse of what happens in the known hot fluid recovery processes, wherein a horizontal flow of hot fluids between injection and production wells is established at a pressure higher than the formation pressure which causes part of the hydrocarbons present between and around the production wells to be left unrecovered in the formation.

As a result of the application of the present method, hydrocarbons flow out of the formation toward the low pressure areas around the production wells. When compared with conventional processes, the new process has an area which can be treated, with a reduced number of wells and with a corresponding reduction of drilling costs.

It should be understood that the present invention is not limited by the particular examples which have been described with reference to the drawing, since many modifications are possible.

The method described above has been successfully employed in the field in oil-bearing formations having hydrocarbons with viscosities between 100 and 1,000 centipoises with significant results.

What is claimed is:

1. A method of producing hydrocarbons from a permeable, hydrocarbon-bearing formation penetrated by at least one injection well and at least one production well, into which formation hot fluid is injected through the injection well, and hydrocarbons are produced through the production well, the improvement comprising reducing the pressure within the pores of the part of the formation contacted by said fluid to a value lower than the pressure within the pores of the rest of said formation subsequent to the breakthrough of said hot fluid into the production well by restricting the rate of injection into the injection well while maintaining a substantially constant output at the production well.

2. A method of producing hydrocarbons from a permeable, hydrocarbon-hearing formation penetrated by at least one injection well and at least one production well, into which formation hot fluid is injected through the injection well, and hydrocarbons are produced through the production well, the improvement comprising reducing the pressure within the pore-s of the part of the formation contacted by the hot fluid to a value lower than the pressure within the pores of the rest of said formation subsequent to the breakthrough of said hot fluid into the production well by decreasing the resistance to flow in the part of the formation surrounding the production well.

3. A method of producing hydrocarbons as claimed in claim 2 wherein a plurality of injection wells and a plurality of production wells are arranged in substantially parallel rows.

4. A method of producing hydrocarbons as claimed in claim 2 wherein a plurality of production wells are arranged around a central injection well.

5. A method of producing hydrocarbons as claimed in claim 2 including the step of simultaneously decreasing the resistance to flow at the outlet of the production well.

6. A method of producing hydrocarbons as claimed in claim 5 including the step of simultaneously increasing the pumping rate of the production well.

7. A method of producing hydrocarbons as claimed in claim 6 including the step of simultaneously decreasing the rate of injection into the injection well while maintaining a substantially constant output at the production well.

8. A method of producing hydrocarbons from a permeable, hydrocarbon-bearing formation penetrated by at least one injection well and at least one production well, into which formation hot fluid is injected through the injection well, and hydrocarbons are produced through the production well, the improvement comprising reducing the pressure within the pores of the part of the formation contacted by the hot fluid to a value lower than the pressure within the pores of the rest of said formation subsequent to the breakthrough of said hot fluid into the production well by increasing the pumping rate of the production well.

9. A method of producing hydrocarbons from a permeable, hydrocarbon-bearing formation penetrated by at least one injection well and at least one production well, wherein each production well has a production tubing arranged therein to protrude below the hydrocarbon-bearing formation, said production tubing being open only at a level below the bottom of the hydrocarbon-bearing formation, into which formation hot fluid is injected through the injection well, and hydrocarbons are produced through the production well, the improvement comprising reducing the pressure within the pores of the part of the formation contacted by said fluid to a value lower than the pressure within the pores of the rest of said formation subsequent to the breakthrough of said hot fluid into the production well.

References Cited UNITED STATES PATENTS 2,813,583 11/1957 Marx et al. 16640 X 2,910,123 10/1959 Elkins et al. 16611 3,136,359 6/1964 Graham 166--4 3,253,652 5/1966 Connally et al 16611 X 3,273,652 9/1966 Huntington 16611 X FOREIGN PATENTS 511,768 8/1939 Great Britain.

STEPHEN J. NOVOSAD, Primary Examiner. 

